Port Blend refers to a wine containing a blend of grapes indigenous to Portugal and typically used for the production of Port. There are 80 different authorised varieties. In the past growers safeguarded the success of their crop by cultivating a field blend, which would contain up to 30 different unidentified varieties. Research conducted in the 1970’s, largely by Ramos Pinto and Cockburn, outlined the most successful of these 80 varieties. Henceforth Touirga Nacional, Tinta Barroca, Touriga Franca, Tinta Roriz and Tinta Cão became regarded as the premier black skinned grapes, along with Tinta Amarela, Mourisco, and Souão. Producers have discovered that magnificent table wines can be produced from these varieties. For White Port Gouveio, Malvasia Fina and Viosinho are considered the finest grapes available.